Typically, conventional detergent compositions contain mixtures of various surfactants in order to remove a wide variety of soils and stains from surfaces. For example, various anionic surfactants, especially the alkyl benzene sulfonates, are useful for removing particulate soils, and various nonionic surfactants, such as the alkyl ethoxylates and alkylphenol ethoxylates, are useful for removing greasy soils.
While the art is replete with a wide variety of surfactants for those skilled in the art of detergent formulation, most of the available suffactants are specialty chemicals which are not suitable for routine use in low cost items such as home laundering compositions. The fact remains that many home-use laundry detergents still comprise one or more of the conventional alkyl benzene sulfonates or primary alkyl sulfate surfactants. Another class of surfactants which has found use in various compositions where emulsification is desired comprises the secondary alkyl sulfates. The conventional secondary alkyl sulfate surfactants are available as generally pasty, random mixtures of sulfated linear and/or partially branched alkanes.
For example, Rossall et al, U.S. Pat. No. 4,235,752, disclose a detergent surfactant which is a C.sub.10-18 secondary alkyl sulfate containing 50% of 2/3 sulfate isomers and 40% of various other effective isomers. The surfactant materials disclosed by Rossall et al is for use primarily in dishwashing operations. Such materials have not come into widespread use in laundry detergents, since they do not offer any advantages over alkyl benzene sulfonates, especially with respect to water solubility which facilitates production of high-surfactant granular detergents. Accordingly, Rossall et al do not provide a high density laundry detergent having improved solubility in either cold temperature wash solutions or high hardness water conditions.
The limited solubility of alkyl sulfate surfactants including both primary and secondary alkyl sulfates is especially prevalent in modern granular laundry detergents which are typically used in cold temperature (e.g. 5.degree. C. to 30.degree. C.) washing solutions and are formulated in "condensed" or "compact" form for low dosage usage. For the consumer, the smaller package size attendant with compact detergent products provides for easy storage and handling. For the manufacturer, unit storage costs, shipping costs and packaging costs are lowered.
The manufacture of acceptable compact or condensed granular detergents has its difficulties. In a typical compact detergent formulation, the so-called "inert" ingredients such as sodium sulfate are substantially eliminated. However, such ingredients do play a role in enhancing solubility of conventional detergents. As a consequence, compact detergents often suffer from solubility problems, especially in cold temperature laundering solutions. Moreover, conventional compact or low density detergent granules are usually prepared by spray drying processes which result in extremely porous detergent particles that are quite amenable to being dissolved in aqueous washing solutions. By contrast, compact detergents are typically comprised of less porous, high density detergent particles which are less soluble, e.g. agglomerates. Thus, since the compact form of granular detergents typically comprise particles or granules which contain high levels of detersive ingredients with little or no room for solubilizing agents, and since such particles are intentionally manufactured at high bulk densities, the net result can be a substantial problem with regard to in-use solubility.
In the art of detergency, the use of hydrotropes have generally been associated with liquid detergent compositions to increase the solubility of various detergent ingredients in the composition. For example, Gutierrez et al, U.S. Pat. No. 4,528,144 (Lever), is directed to a liquid detergent compositions containing terpene sulfonate hydrotropes and various other detergent ingredients. In a similar fashion, Lamberti et al, U.S. Pat. No. 4,623,483 (Lever), is also directed to a liquid detergent composition comprising a hydrotrope and other conventional detergent ingredients. Both of the Lamberti et al and Gutierrez patents only suggest processes for making "liquid" compositions and are silent with respect to processing granular or agglomerated versions of the detergent disclosed therein. Thus, these patents do not speak to the solubility problem associated with cold temperature laundering solutions, a problem particularly prevalent when using detergents which are not spray-dried.
Accordingly, despite the disclosures in the art, there remains a need for a process for making a detergent composition which has improved solubility, especially in cold temperature washing solutions. This need is especially prevalent in the art of compact or high density detergents currently being used by consumers. There is also a need for such a process which produces a detergent composition having improved solubility under high water hardness conditions. Also, there is a need for such a process resulting in a detergent composition having improved biodegradability.